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Alexei Popov
alexei.a.popov@gmail.com

this can be done very simple.

Run single point SCF energy calculation. Look at the output and you'll see strings like these:

TOTAL NUMBER OF SHELLS              =   10
TOTAL NUMBER OF BASIS FUNCTIONS     =   38
NUMBER OF ELECTRONS                 =   12
CHARGE OF MOLECULE                  =    0
STATE MULTIPLICITY                  =    1
NUMBER OF OCCUPIED ORBITALS (ALPHA) =    6
NUMBER OF OCCUPIED ORBITALS (BETA ) =    6

Orbital #6 is HOMO and orbital #7 is LUMO.

Look at the section

FINAL ENERGY IS....


         ------------
         EIGENVECTORS
         ------------

and find the eigen-vectors #6 and #7 (they are numbered so it is easy)
The numbers above the eigen-vectors are their energies. Substract two numbers for two orbitals and you'll get the answer.

Cheers,
Alexei Popov



On Mon Feb 4 '13 12:41pm, Siddheshwar Chopra wrote
--------------------------------------------------
>Dear Sir,
>Please forgive me for asking this question perhaps again in this forum. Actually I have completed the HESSIAN run and am able to read the HOMO,LUMO energies USING GABEDIT software. But I find it really too involving and error prone to calculate the HOMO-LUMO gap from the data. Please suggest em a simpler way so that I get the HOMO-LUMO gap directly...IS there any COMMAND I could add in the FIREFLY input file to get HOMO-LUMO printed in the output file directly?
>If a command line input is not available, can Prof. Alex add ONE such command for the users?

>Regards,